This invention relates to aluminum alloy vehicular members and more particularly, it relates to a method of casting aluminum alloy into sheet having good forming characteristics and to forming the sheet into vehicular frame members.
In many instances, continuous casting of molten aluminum into slab utilizing twin belt or twin roll casters is favored over D.C. casting because the twin belt or twin roll casting can result in substantial energy savings and total conversion cost savings compared to the D.C. cast method. In the twin belt or twin roll process, molten metal is continuously introduced to an advancing mold and a slab is produced which may be continuously formed into a sheet product which is collected or wound into a coil. However, the continuous casting is not without problems. For example, it has been discovered that the alloy composition and the processing steps must be carefully controlled in order to have the formability level to avoid cracking during forming and yet have the requisite strength properties in the final product. That is, the alloy and the processing thereof must be carefully controlled to provide sheet having the formability suited to the fabricating steps necessary to form the final product or vehicular member. If the alloy and processing steps are not controlled, then in the forming steps, fracture can occur and the formed parts have to be scrapped. Thus, there is a great need for selection of an aluminum alloy, continuous casting thereof, and thermal mechanical processing methods which provide a sheet product having forming characteristics and strength properties which permit forming operations such as hydroforming for producing vehicular members while avoiding problems of fracturing or cracking, for example.
The continuous casting of molten aluminum and rolling slab produced therefrom into a sheet product is disclosed in various patents. For example, U.S. Pat. No. 5,976,279 discloses a process for continuously casting aluminum alloys and improved aluminum alloy compositions. The process includes the steps of continuously annealing the cold rolled strip in an intermediate anneal using an induction heater and/or continuously annealing the hot rolled strip in an induction heater. The alloy composition has mechanical properties that can be varied selectively by varying the time and temperature of a stabilizing anneal.
U.S. Pat. 6,264,765 discloses a method and apparatus for casting, hot rolling and annealing non-heat treatment aluminum alloys. The method and apparatus comprises continuous casting, hot rolling and in-line inductively heating the aluminum sheet to obtain the mechanical properties within the specification tolerance of the hot rolled product.
U.S. Pat. No. 5,985,058 discloses a process for continuously casting aluminum alloys and improved aluminum alloy compositions. The process includes the step of heating the cast strip before, during or after hot rolling to a temperature in excess of the output temperature of the cast strip from the chill blocks. The alloy composition has a relatively low magnesium content yet possesses superior strength properties.
U.S. Pat. No. 5,993,573 discloses a process for continuously casting aluminum alloys and improved aluminum alloy compositions. The process includes the steps of (a) heating the cast strip before, during or after hot rolling to a temperature in excess of the output temperature of the cast strip from the chill blocks and (b) stabilization or back annealing in an induction heater of cold rolled strip produced from the cast strip.
U.S. Pat. No. 5,833,775 discloses an aluminum alloy sheet and a method for producing an aluminum alloy sheet. The aluminum alloy sheet is useful for forming into drawn and ironed container bodies. The sheet preferably has an after-bake yield strength of at least about 37 ksi and an elongation of at least about 2 percent. Preferably the sheet also has earing of less than about 2 percent.
U.S. Pat. No. 6,086,690 discloses a process of producing an aluminum alloy sheet article of high yield strength and ductility suitable, in particular, for use in manufacturing automotive panels. The process comprises casting a non heat-treatable aluminum alloy to form a cast slab, and subjecting said cast slab to a series of rolling steps to produce a sheet article of final gauge, preferably followed by annealing to cause recrystallization. The rolling steps involve hot and warm rolling the slab to form an intermediate sheet article of intermediate gauge, cooling the intermediate sheet article, and then warm and cold rolling the cooled intermediate sheet to final gauge at a temperature in the range of ambient temperature to 340xc2x0 C. to form said sheet article. The series of rolling steps is carried out continuously without intermediate coiling or full annealing of the intermediate sheet article. The invention also relates to the alloy sheet article produced by the process.
U.S. Pat. No. 5,244,516 discloses an aluminum alloy plate for discs superior in Nixe2x80x94P platability and adhesionability of plated layer and having a high surface smoothness with a minimum of nodules and micropits, said aluminum alloy plate comprising an aluminum alloy containing as essential elements Mg in an amount more than 3% and equal to or less than 6%, Cu in an amount equal to or more than 0.03% and less than 0.3%, and Zn in an amount equal to or more than 0.03% and equal to or less than 0.4%, and as impurities Fe in an amount equal to or less than 0.07% and Si in an amount equal to or less than 0.06% in the case of semi-continuous casting, or Fe in an amount equal to or less than 0.1% and Si in an amount equal to or less than 0.1% in the case of strip casting, and also containing Alxe2x80x94Fe phase intermetallic compounds, with the maximum size being smaller than 10 xcexcm and the number of particles larger than 5 xcexcm being less than 5 per 0.2 mm2, and Mgxe2x80x94Si phase intermetallic compounds, with the maximum size being smaller than 8 xcexcm and the number of particles larger than 5 xcexcm being less than 5 per 0.2 mm2.
U.S. Pat. No. 5,514,228 discloses a method for manufacturing aluminum sheet stock which includes hot rolling an aluminum alloy sheet stock, annealing and solution heat treating it without substantial intermediate cooling and rapid quenching.
In spite of these disclosures, there is a great need for selection of aluminum alloy and method for producing vehicular parts or members utilizing a continuous caster, thermal mechanical processing, to provide good strength and levels of formability which forming into intricate parts without cracking.
The term xe2x80x9cformabilityxe2x80x9d when used herein is used to describe the ease with of metal can be shaped through plastic deformation. Formability of a metal ted by measuring strength, ductility, and the amount of deformation to cause failure.
The term xe2x80x9caluminumxe2x80x9d when used herein is meant to include aluminum and its alloys.
The term xe2x80x9cautomotivexe2x80x9d as used herein is meant to include automobile and other vehicular members such as truck frame members and other transport members having similar construction.
It is an object of the invention to provide an improved, low cost process including continuous casting and rolling to continuously produce aluminum sheet product having consistent levels of formability.
It is another object of the invention to provide a process including continuously casting a slab and rolling the slab into a sheet product suitable for use in producing vehicular parts.
It is still another object of the invention to provide a process employing continuous casting of molten aluminum into slab and rolling the slab into sheet product for forming tube products suitable for hydroforming into vehicular frame members.
And yet it is another object of the invention to provide an improved process for producing aluminum sheet product employing a continuous caster to produce slab, continuously rolling the slab to produce a sheet product and annealing the sheet product for forming into vehicular parts or members.
It is another object of the invention to provide a process for producing vehicular members such as frame members which includes continuously casting an aluminum alloy into a slab and rolling the slab to a sheet product having good levels of formability.
It is yet another object of the invention to provide a process for producing vehicular members such as frame members which includes continuously casting an aluminum alloy into a slab and rolling the slab to a sheet product having good levels of formability, forming the sheet product into a tube which is welded and hydroformed into a vehicular member.
And yet it is another object of the invention to provide a process for casting a molten alloy comprising 2.7 to 3.6 wt. % Mg, 0.1 to 0.4 wt. % Mn, 0.02 to 0.2 wt. % Si, 0.05 to 0.30 wt. % Fe, 0.1 wt. % max. Cu, 0.1 wt. % max. Cr, 0.2 wt. % max. Zr, the remainder aluminum, incidental elements and impurities, casting the alloy into a slab which is hot rolled and annealed to provide a sheet product which is hydroformed into a vehicular member such as a frame member.
In accordance with these objects, there is provided a process for producing aluminum vehicular members such as frame members from molten aluminum alloy using a continuous caster to cast the alloy into a slab. The method comprises providing a molten aluminum alloy consisting essentially of 2.7 to 3.6 wt. % Mg, 0.1 to 0.4 wt. % Mn, 0.02 to 0.2 wt. % Si, 0.05 to 0.3 wt. % Fe, 0.1 wt. % max. Cu, 0.1 wt. % max. Cr, 0.2 wt. % max. Zr, the remainder aluminum, incidental elements and impurities and providing a continuous caster such as a belt caster for continuously casting the molten aluminum alloy. The molten aluminum alloy is cast into a slab having Alxe2x80x94Fexe2x80x94Mn-containing intermetallic particles. The slab is rolled into a sheet product which is then annealed to provide a sheet product having substantially uniform distribution or reduced striations of the intermetallic particles for improved formability and corrosion resistance. Thereafter, the sheet product is formed into a tube having a seam which is welded to provide a seam welded tube. The seam welded tube is placed in a forming die and hydroforned to form the frame member.
Alternatively, the hot rolled sheet may be cold rolled after hot rolling, and then annealed prior to the forming steps. In yet another embodiment, the hot rolled sheet may be annealed or even homogenized and then cold rolled to a cold rolled sheet product. The cold rolled product can be annealed to provide a product suited to the various forming steps.
These and other objects will become apparent from a reading of the specification and claims appended hereto.